Environmental problems increasing worldwide, increasing energy demand and resource shortages require new technologies for power plants which on the one hand side continuously increase the overall percentage of renewable energies and on the other hand side assures continuous energy supply. The new technologies among other things include hybrid power plants which operate on various combinable and exchangeable energy sources.
Among the conventional power plants are steam power plants, gas turbine power plants and combined gas-steam power plants in which the principles of a gas turbine power plant and a steam power plant are combined. They are used for conventionally generating electrical energy from fossil fuels. In a steam power plant in which the fossil fuels are used for evaporating water, the thermal energy of the water vapor is transformed into electrical energy through a steam turbine which in turn drives a generator. In a gas turbine power plant, a gas turbine is operated with liquid or gaseous hydrocarbon based fuel like, for example, natural gas. The gas turbine itself also drives a generator for power generation. The exhaust gases of the gas turbine have high temperature and can thus be used for additionally heating a waste heat boiler in the gas-steam hybrid power plant. In a combined cycle gas-steam power plant, a gas turbine, besides directly generating electrical energy from fossil fuels, is also used as a heat source for the subsequent waste heat boiler which functions as a steam generator for the steam turbine. The steam is subsequently expanded through a conventional steam turbine process.
Besides using the waste heat of the gas turbine, the steam power and thus the electrical power of the steam turbine can be increased by additionally heating the boiler. Solar-thermal steam generation is another option for additional heating. This type of steam generation based on using solar energy is possible in the recited combination with a combined cycle gas-steam power plant, a fossil fuel steam power plant with solar heat coupling or as a standalone solar thermal power plant. In a solar thermal power plant, the radiation energy of the sun is coupled into the power plant cycle through a receiver also designated as absorber or collector and is thus being used as a primary energy source. Thus, the radiation energy of the sun is used for energy generation by focusing direct radiation through reflectors onto the solar receiver. The reflectors include surfaces concentrating the incident sunlight. The receiver or the reflectors are typically tracked after the sun. In solar tower power plants and parabolic channel power plants which are particular embodiments of solar thermal power plants, sun radiation is focused through reflectors.
Solar tower power plants are typically steam power plants with solar steam generation. A steam generator which is heated in a conventional steam power plant through fossil fuels like oil, natural gas or coal is replaced by a solar steam generation unit, a receiver or absorber on a tower. When the sun shines, automatically positioning mirrors, so-called heliostats, align so that the sunlight is reflected onto the central receiver. Therein the radiation energy is transmitted to a heat transfer medium like air, liquid salt or the process medium water/steam in the form of heat. The heated heat transfer medium is then used, for example, for generating steam in a steam turbine power plant and for subsequent electric energy generation through a generator coupled with a turbine.
The development of parabolic channel power plants which are already mostly being used in regenerative power plants and also in so-called ISCC power plants (Integrated Solar Combined Cycle) is the most advanced with respect to solar thermal power plants. Parabolic channel power plants due to the comparatively small temperature level have the advantage that heat storage for process safety can be implemented in a rather simple manner. The limited upper process temperatures, however, on the other hand side are disadvantageous for efficiency and cost. Solar operated units combined with steam cycle processes are known in the art.
DE 196 27 425 A1 discloses a hybrid solar combined cycle unit, including a gas turbine unit, a steam turbine unit, a waste heat steam generator and a solar steam generator. The unit is configured for hybrid-solar combined operation, pure solar operation and combined operation. In hybrid-solar combined operations, the solar vapor generator is used as an additional steam generator besides the waste heat steam generator. For pure solar operations and combined operations, the steam is either provided in the solar steam generator or in the waste heat-steam generator. The steam generated is respectively used for operating the steam turbine. The heat generated through solar energy is exclusively coupled into the steam process. A similar embodiment of a solar operated unit with gas and steam turbine is disclosed in U.S. Pat. No. 5,444,972 A. The solar heat coupled into the cycle of a heat transfer medium through a solar receiver is additionally provided for steam generation in the waste heat boiler besides the exhaust heat of the gas turbine. Also in this unit, the solar heat is only being used in the steam cycle.
DE 41 26 036 A1, DE 41 26 037 A1 and DE 41 26 038 A1 disclose gas and steam turbine power plants with additional devices for solar steam generation, which are respectively connected to a feed water supply of a steam turbine power plant. The device for solar steam generation according to DE 41 26 036 A1 leads into the high pressure steam conduit running from the waste heat steam generator to the steam turbine, so that the steam generated at the high pressure super heater heating surfaces of the waste heat steam generator is mixed with the steam of the solar steam generator and conducted to the steam turbine.
In the power plant disclosed in DE 41 26 037 A1 and also in the power plant disclosed in DE 41 26 038 A1 the solar steam generation unit is directly connected to the high pressure super heater heating surfaces of the waste heat steam generator. The power plant disclosed in DE 41 26 037 A1 furthermore includes a high pressure, medium pressure and low pressure steam turbine. Thus, solar steam generation is additionally connected with the medium pressure steam unit of the steam turbine process. In the recited gas and steam turbine power plants, the heat generated through a solar process is only fed to the steam turbine process.
DE 20 2008 002 599 U1 discloses a solar thermal hybrid power plant with a solar thermally heated heat transfer medium cycle and a steam/water cycle of a turbine stage thermally coupled with the steam generation stage. The steam/water cycle includes a super heater that is connected downstream of the solar thermal super heater and decoupled from the heat transfer medium cycle. The heat transfer medium cycle is closed. Thermal oil or water are being used as heat transfer media, wherein heat from the heat transfer medium is transferred in heat-exchangers to the actual steam turbine process. The power plant with solar thermal heat induction is a pure steam power plant.
Furthermore a gas turbine unit with solar heat coupled into the process is known in the art. The solar hybrid gas turbine unit is a piece of experimental equipment with a modified helicopter engine which is arranged in a solar tower and in which the combustion air is heated through solar radiation between a compressor outlet and a combustion chamber inlet. The gas turbine is arranged in the tower proximal to the receivers and thus unsuitable for larger units.
U.S. Pat. No. 5,417,052 discloses a gas and steam turbine power plant in combination with solar heat coupling into the gas turbine unit. The solar radiation energy converted into thermal energy through a solar receiver is transported through a heat transfer medium from the receiver to a heat transfer medium which is provided for heating the compressed combustion air. The air heated through solar energy is subsequently supplied to the combustion chamber. The solar heat generated is thus exclusively coupled into the gas process.
Solar thermal power plants either in combination with steam turbine units or in combination with gas turbine units are known in the art, but they have various disadvantages. Thus, high process temperatures and thus high percentages of solar heat induction combined with different primary energies can only be facilitated on a limited basis. The desired high process temperatures furthermore counteract an option to store heat so that mostly fossil fuels have to be used for heating when there is low solar radiation. On the other hand side low process temperatures cause low efficiency. For high process temperatures in turn, only a small percentage of the heat induction into the hybrid power plant can be implemented. For these reasons so far a disadvantageous compromise is made between high process temperature, solar portion of heat induction and supply safety or supply quality with respect to electric energy.
Furthermore the use of gas turbine units with solar heat coupled into the process is limited to small units as long as the gas turbine has to be positioned proximal to the receiver.